According to a UPI wire story from Saigon which ran in American newspapers beginning Monday, September 27,
The Viet Cong said they executed two American prisoners Sunday … Although the broadcast did not say so, the executions apparently were in retaliation for the deaths Thursday of three anti-American demonstrators. The demonstrators were convicted by a military tribunal of engaging in terrorist activities and put before a firing squad in a soccer stadium at Da Nang.
An earlier execution of a Viet Cong terrorist by the government June 24 brought an announcement from the Communists that they had executed Sgt. Harold G. Bennet[t], a captive from Arkansas.
The two men shot on September 26 — whose names are garbled in the initial news report, since “the names were received phonetically” — were Sgt. Kenneth Mills Roraback and Capt. Humbert Roque “Rocky” Versace.